Material used for spring connection devices must exhibit ability to maintain adequate contact pressure for the design life of any part formed from the material. The maintenance of adequate contact pressure requires the ability of the material to resist stress relaxation over a period of time especially at elevated temperatures above normal room temperature. The current trend in connector design has been to place greater emphasis upon the maintenance of high contact pressure on connector parts at mildly elevated temperatures to reduce problems which might develop as the surface temperatures of the parts increase. CDA Alloy C68800 is currently widely used for electrical connectors but tends to exhibit a less than desired stress relaxation resistance at temperatures of 75.degree. C. or higher. Accordingly, it is desirable that alternative alloys be provided having improved elevated temperature stress relaxation performance.
It is important in any such alloys that a reasonable level of conductivity be maintained along with the improved stress relaxation performance. Furthermore, bend formability should be maintained as well as the other desirable strength properties of CDA Alloy C68800. Other performance characteristics such as stress corrosion, solderability and softening resistance should not be significantly below those properties exhibited by the commercial CDA Alloy C68800. It is desired in accordance with this invention that the improved alloy exhibit approximately a 10 to 30% increase in projected stress remaining after 100,000 hours at 105.degree. C. relative to the commercially available CDA Copper Alloy C68800. That alloy is included within the limits of U.S. Pat. No. 3,402,043 to Smith.
It has surprisingly been found that when an alloy as disclosed in U.S. Pat. No. 3,816,187 to Smith is modified through the addition of manganese within specific limits its stress relaxation performance is substantially improved while maintaining excellent strength and bend properties and with a limited degree of conductivity loss. In the Smith U.S. Pat. No. 3,816,187 manganese is disclosed for addition only as a common impurity.
Various attempts have been made to improve the stress relaxation performance of CDA Copper Alloy C68800 and related alloys and also to improve other properties of these alloys by modification of their processing as exemplified in U.S. Pat. Nos. 3,841,921 and 3,941,619 to Shapiro et al. and 4,025,367 to Parikh et al. The Shapiro et al. U.S. Pat. No. 3,841,921 patent is particularly pertinent in that it deals with improving the stress relaxation resistance of the desired alloys which are broadly defined and which may include up to 10% manganese as one of many possible alternative alloying additions.
U.S. Pat. No. 1,869,554 to Ellis is of interest and it discloses a brass alloy including 2 to 7% manganese. The alloy comprises a beta or alpha plus beta alloy and generally includes a level of zinc well above that included in the alloy of the present invention. In U.S. Pat. No. 3,764,306 to Blythe et al. a prior art alloy is disclosed comprising an aluminum-brass including from 6 to 30% manganese.
In U.S. Pat. No. 2,101,930 to Davis et al. an aluminum-brass is disclosed having optionally up to 1% manganese. In U.S. Pat. No. 2,400,234 to Hudson a nickel-aluminum-brass is disclosed having from 0.5 to 2.5% manganese. None of the patents to Ellis, Blythe et al., Davis et. al. and Hudson disclose an alloy within the ranges of this invention.
British Pat. No. 833,288 discloses a beta brass including aluminum, iron and nickel or cobalt and optionally manganese. British Pat. No. 838,762 discloses a copper, zinc, titanium and/or zirconium alloy which may include 0.25 to 2% of one or more of the metals chromium, manganese, iron, cobalt and nickel.